"An error occurred when trying to create a controller of type 'AnalyticsDataController'. Make sure that the controller has a parameterless public constructor."
"at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType) at System.Web.Http.Controllers.HttpControllerDescriptor.CreateController(HttpRequestMessage request) at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()"

That results to several icons missing from Launchpad, for example FXM.

That is exact point of my confusion I've experienced previous week, when Sitecore 8.1 was released. The explanation is below:

Previously in Sitecore 8.0, there was a very confusing situation, when many new features introduced in 8.0 required license for 8.0. Running those features with a license from one of previous Sitecore version did not block those features in UI from working, but still disabled them from inside of CMS. That lead to some confusing situations like I have described in one of my previous blog posts (see: blog post about FXM and question on StackOverflow) when user without appropriate license ran FXM and couldn't add parent placeholder - no relevant error message was said.

Now since 8.1, Sitecore decided to perform very reasonable structural changes to separate CMS from xDB and Analytics with licensing model. They introduces a new CMS-only mode when Sitecore can run without xDB and Mongo, just CMS features. Those who require to use xDB and Analytics in 8.1 now need to request explicit license allowing those features (using this URL). Otherwise their Sitecore instance will default to CMS-only mode. Sitecore download page contains a warning message regarding those changes:

Sitecore 8.1 now requires a license with the “Sitecore.xDB” key to enable all features of the Experience Platform. If your license file does not contain this key, Sitecore will default to Experience Management (CMS-only) mode. Any customers or partners with a license to Experience Platform should contact their account manager or login to SPN if they are missing this key.

But what about javasript errors? Well, that is definitely a bug. I have previously contacted Sitecore support in order to report a bug (issue Id 451464). Even if you explicitly enable CMS-only mode in Sitecore.xDB.config - you'll still get those AJAX errors. It looks that corresponding SPEAK controls try to call to Entity Services (web API) and it returns generic 500-error (internal server error) code, instead of something more specific like 403 (forbidden) and proper handling that code in JavaScript on client side.

Hope Sitecore fixes that shortly!

Update: I have received confirmation that having a license for xDB in 8.1 this issue does not occur.